1. Field of the Invention
The present invention relates to an air relief device disposed in any of various kinds of liquid flow pipes such as supply pipes for cooling water and liquid material in plant equipment, water mains, etc.
2. Description of the Prior Art
The air present in a liquid flow pipe is one of the largest factors of obstructing the flow of liquid. For this reason, an air relief device utilizing a float valve mechanism is generally disposed in the liquid flow pipe, particularly in a portion of the liquid flow pipe arranged at an elevation.
When the flow pipe is exhausted of air by utilizing the float valve mechanism, however, since suspended matter, such as dust etc., contained in the liquid flows together with the air into the valve casing of the float valve mechanism, it is necessary to clean the interior of the valve casing. Further, this cleaning work must be carried out in a state wherein the fluid communication between the valve casing and the flow pipe is cut off.
For this reason, a prior art air relief device comprises a valve casing having a float valve mechanism arranged therein and a switch valve interposed between the valve casing and a flow pipe, and has a construction such that fluid communication between the flow pipe and the valve casing is cut off by the switch valve when the valve casing is to be cleaned.
However, the construction having the switch valve interposed between the valve casing and the flow pipe causes the valve casing to project for nothing upwardly from the flow pipe and, due to the smaller size of the switch valve as compared with that of the valve casing, to project upward in a considerably ill-balanced state, i.e. in a top-heavy state. Therefore, the prior art air relief device per se is set in position in a state of being liable to be damaged or broken down by an impact etc.
Since the valve casing of the prior art air relief device is far from the flow pipe due to the interposition of the switch valve therebetween and since the liquid stays within the valve casing, particularly when the air relief device is used in a cold district, the staying liquid is liable to be frozen. For example, there is a case where a heat insulation cover is required to be attached to the valve casing in order to avoid freezing of the staying liquid. However, since the prior art air relief device is protruded in an ill-balanced state, the heat insulation cover becomes complicated in shape and is cumbersome to attach.